Conventional computed tomography (CT) exposes the patient to large doses of radiation, which create health risks, particularly if a patient undergoes many CT scans. The dosage in even a single CT procedure may be undesirable. For example, in some circumstances, a CT scan of the abdomen and pelvis (repeated with and without contrast material) exposes the patient to 20 mSv of radiation, which is the equivalent of 7 years of natural background radiation and is considered to create a moderate risk of cancer.
Even conventional radiographs (loosely called “X-rays”) expose the patient to substantial doses of radiation, which if repeated over time, may have a cumulative effect that is harmful to health. For example, in some circumstances, a conventional radiograph of the spine exposes the patient to 1.5 mSv of radiation, which is the equivalent of 6 months of natural background radiation.
It is desirable to image tissue with X-rays, in a manner that sharply reduces the radiation dosage to the patient.